TEST 2: Verifying The Heater Element Is Getting Ground

3-Wire Oxygen Sensor Heater Test -P0141 (1993 3.8L V6 GM)

Now that you've confirmed that the oxygen sensor's heater is being fed with power, the next step is to make sure that it's getting chassis ground.

The black (BLK) wire, of the engine wiring harness O2 sensor's electrical connector, is the one that supplies this chassis ground to the 3-wire oxygen sensor.

We can do a very simple multimeter voltage test to see if ground is indeed present or not.

IMPORTANT: The pinout in the illustration above is of the connector on the oxygen sensor itself. To check for power, you need to test the BLK wire of the engine wiring harness sensor connector.

These are the test steps:

  1. 1

    Locate the BLK wire of the O2 sensor's engine wiring harness connector.

    NOTE: Remember, you'll test the wire that's on the engine wiring harness connector side and NOT on the O2 sensor itself.

  2. 2

    Place your multimeter in Volts DC mode and connect the red multimeter test lead to battery (+).

    With the black multimeter test lead, probe the BLK wire of the O2 sensor's harness connector.

  3. 3

    With the Key On, engine Off, this wire should have 10 to 12 Volts DC.

Let's take a look at your test results:

CASE 1: The multimeter confirms that the BLK wire is feeding ground since it registered 10 to 12 Volts DC- This confirms the 3-wire O2 sensor's heater is being fed with ground.

So far you've confirmed that the 3-wire O2 sensor's heater element is getting both power and ground. The next step is to check the heater element's resistance with your multimeter...for this test, go to TEST 3: Testing The Heater Element's Resistance.

CASE 2: The multimeter confirms that the BLK wire IS NOT feeding ground since it DID NOT register 10 to 12 Volts DC- Re-check all of your connections and make sure you're testing the correct terminal.

If your multimeter still doesn't register the 10 to 12 Volts DC, then the most likely cause of this missing ground is an ‘open’ in the BLK wire between the O2 sensor's harness connector and chassis ground.

TEST 3: Testing The Heater Element's Resistance

3-Wire Oxygen Sensor Heater Test -P0141 (1993 3.8L V6 GM)

Having checked the basics, which are:

  1. The PNK/BLK wire has 10 to 12 Volts DC (TEST 1).
  2. The BLK wire is feeding the 3-wire O2 sensor with ground (TEST 2).

In this last test section we're gonna' verify that the 3-wire O2 sensor's heater resistance is within factory specification.

If the resistance is not within specification, then we now know the O2 sensor is bad and needs to be replaced.

NOTE: Just a reminder that the 3-wire oxygen sensor has to be completely cold before proceeding with this test since the manual calls for the O2 sensor to be at room temperature for the resistance test.

OK, this is what you need to do:

  1. 1

    Locate the O2 sensor terminals A and B of the O2 sensor connector itself (not the engine wiring harness O2 connector).

  2. 2

    With your multimeter in Ohms mode... probe terminals A and B of the O2 sensor itself.

  3. 3

    If all is OK, you should see about 3.5 to 14 Ωs on your multimeter.

    If the heater element is fried, your multimeter will show an open (usually indicated by the letters OL) or a number over 10 K Ωs.

Let's take a look at your test results:

CASE 1: The 3-wire O2 sensor's heater resistance is within spec.- This test result tells you that oxygen sensor's heater is OK.

CASE 2: Your multimeter showed an open circuit (OL)- This confirms that the O2 sensor's heater element is fried and needs to be replaced with a new one.

Here are some more specifics: Since you have:

  1. Confirmed that the 3-wire O2 sensor's heater element is getting power (TEST 1).
  2.      -AND-
  3. Confirmed that the 3-wire O2 sensor's heater element is getting ground (TEST 2).
  4.      -AND-
  5. In this test you have confirmed that the heater element's resistance is out of specification.

Taking all of the above into account you can correctly conclude that the 3-wire O2 sensor needs to be replaced with a new one.